1. Field of the Invention
This invention relates to hybrid rocket motors. More specifically, the present invention relates to a method for improving combustion efficiency of simple fuels (e.g. hydrocarbon polymers or rubbers) in a hybrid rocket motor utilizing direct oxidizer injection.
2. Technology Background
Hybrid rocket motors utilize solid fuel and fluid oxidizer. The fuel and oxidizer are kept separated until it is desired to operate the motor, at which time the oxidizer is usually injected into the motor to mix with the fuel during operation. It is desirable that the solid fuel extinguish when oxidizer flow is terminated and that the regression rate of the fuel be directly proportional to the oxidizer flow rate, i.e. that the system can be throttled.
By contrast, solid propellants integrally mix the fuel and oxidizer together. Solid propellants are useful because of their ease of storage in which the propellants can be cast or molded into a desired form and stored until time for use. The disadvantage is that once ignited, the propellant burns until exhausted since there is no reliable means to extinguish the rocket and then reignite it. Liquid propellants using liquid fuel and liquid oxidizer permit control of the rocket motor combustion by simply controlling the fuel and oxidizer flow rates. A disadvantage of liquid propellants is the difficulty of liquid storage and complex fluid control mechanisms.
Hybrid rocket motor development has been evolving for a number of years. One of the most difficult technologies encountered during development of hybrid rocket motors has been the achievement of sufficiently high solid fuel regression during motor operation to allow simple grain geometries and high propellant mass fractions to be employed in motor design. In achieving this end, a multitude of fuel additives and formulations, including reactive metals, oxidizers, and catalysts have been investigated in hybrid motor development programs using liquid or gaseous oxidizer injection.
Unfortunately, the above approaches suffer from significant safety and handling considerations. In general, use of solid oxidizer at levels sufficient to achieve the desired regression rate enhancements in the fuel grains results in compositions capable of sustaining low level combustion in the absence of supplemental oxidizer making these behave as conventional solid propellants. Use of reactive metals can raise problems in fuel grain processing and storage due to moisture and air sensitivity. Other additives, such as fluorine or perchlorate in the propellant system, result in acidic and toxic hydrogen halides in the exhaust, which can result in environmental damage, particularly with large booster motor applications. Thus, known methods of improving hybrid motor ballistic properties suffer from undesirable side effects, such as component toxicity and hazards, and environmental effects from exhaust products.
It will be appreciated that there is a need in the art for methods and apparatus for improving combustion efficiency and regression rate of fuels in a hybrid rocket motor without undesirable toxicity, safety, and environmental effects. It would also be an advancement in the art to provide methods and apparatus for enhanced hybrid combustor operation which utilize inexpensive, simple fuels.
Such methods and apparatus for improving combustion efficiency and regression rate of simple fuels in hybrid rocket motors are disclosed and claimed herein.